MKC84LU006

Before the flt, the instructor saw a thunderstorm approximatetly 20 mi north of the field, moving slowly to the south-southeast. He & the student elected to make a short flt. After taking off, they made a practice forced landing in an open field about 1 mi northwest of the departure point. After the forced landing, they start another takeoff run. At the same time the tail was raised during the roll, a sudden gust of wind was encountered. The instructor said the air was dead calm, then 1 sec later, it gusted to 40 mph. He said that the ultralight went straight up in a flat climb, much like a helicopter. After reaching an estimated 200 ft AGL, the rough air reportedly rolled the ultralight into a 90 deg left bank & it began a fast descent. Subsequently, the vehicle impacted in a shallow pond while traveling about 50 mph. The student was wearing a motorcycle helmet & stated that it saved him from having a serious head injury.